This PR adds the `correctly_deleted_chars` field and updates `kept_rate`
to account for it, not just inserted chars.
It also adds `recall_rate` to measure coverage of reference
insertions/deletions.
Finally, it renames "final" to "reference" and "prediction" to
"candidate".
Self-Review Checklist:
- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable
Release Notes:
- N/A
Oleksiy Syvokon
148317aa5d